Rubber expansion joints are widely used in general service piping systems including water supply, fire protection, chill water and drain for the purpose of absorbing linear movements generated by thermal expansion and/or contraction, lateral sways caused by earthquakes, vibration and noises in the pump room, and the like.
A rubber expansion joint may be formed of a rubber bellow(s), as shown in FIGS. 1 and 2, coupled with a pair of steel (or iron) flanges for connection to existing piping systems, because rubber bellows cannot otherwise presently be directly connected with pipes to create a non-leaking union. Rubber is elastic but not very strong against thrust load and inner pressures and is therefore generally reinforced with layers made of nylon fabrics or steel braiding.
Such a flanged rubber expansion joint requires a counter flange at each end to be mounted on the pipe end and requires a number of bolts and nuts for connection (see FIG. 3). In the flanged rubber expansion joint, the flanges placed outside of the bellow(s) serve not only as connectors with counter flanges but also as retainers of the bellow(s) from slippage. Both ends of the bellow(s) are sandwiched in between the flanges and secured by tightening of the bolts and nuts.
However, installation of a flange on a pipe end requires welding with high temperature flames or arcs. And as the use of a flame or arc is believed to be an accidental fire hazard, welding at job sites is nowadays entirely prohibited or strictly restricted. The present alternative for installing a flanged rubber expansion joint in a grooved-ended piping system is to prepare a couple of special adapters like the ones shown in FIG. 4, but that requires extra pieces and extra work and pushes up the cost.
In recent years, grooved-ended piping systems have come into wide use and acceptance as they provide high work efficiency without the use of flames or arcs at job site. What has not been developed is a grooved-end rubber expansion joint which enables a direct connection with coaxial grooved-end pipes, without the use of flanges.